From German patent application 1,964,469 (U.S. Pat. No. 3,676,004) an atomic absorption spectrometer is known wherein the radiation originates from a single light source designed as a line emitter, the radiation of which passing through the sample is frequency modulated by use of the longitudinal Zeeman effect. In this prior atomic absorption spectrometer a hollow cathode lamp is arranged between the pole pieces of an electromagnet. One of the pole pieces has a bore through which the measuring light beam passes. Then the measuring light beam is directed through a flame serving as an atomizing device and a monochromator and impinges upon a photoelectric detector. The electromagnet is arranged to be switched on and off, whereby the atomic absorption of the sample atoms compensated for with respect to the background absorption can be determined from the difference between the signals with the electromagnet switched off and switched on. The windings of the electromagnet are provided on the pole pieces.
In this prior art atomic absorption spectrometer the emission lines of the line emitting light source are periodically shifted by the Zeeman effect and thus the emitted light frequency is modulated and not the absorption lines of the sample. This may cause problems when a hollow cathode lamp is used as a light source because the discharge of the hollow cathode lamp is influenced by the magnetic field, as already mentioned in German Patent Application 1,964,469,
From German patent application 2,165,106 it is known to apply the magnetic field of an electromagnet arranged to be switched on and off to the atomizing device, i.e. to the sample which is to be atomized, instead of to the light source. Therein the atomizing device is a flame. The magnetic field is applied perpendicular to the direction of the propagation of the measuring light beam. A splitting of the absorption lines due to the "transverse" Zeeman effect is effected, which again causes a relative shift of the emission lines of the measuring light beam and the absorption lines of the sample. Again, it is possible to discriminate between atomic absorption by the atoms of the element looked for and non-specific background absorption by switching the magnetic field on and off.
When the transverse Zeeman effect is used, a spectral line is split into a central line, the wave length of which corresponds to the non-shifted wave length of the respective line with the magnetic field switched off and two side lines which relative thereto are shifted to longer and shorter wave lengths. The central line and the side lines are polarized differently. Therefore, the influence of the central line can be eliminated by a polarizer.
In the prior art atomic absorption spectrometer a magnetic field causing the Zeeman effect is generated by an electromagnet which is excited by one-way rectified mains A.C. voltage. A narrow area of the half wave of the mains A.C. voltage around the maximum of the half wave is used for measuring the background absorption when the Zeeman effect occurs. Thereby, a relatively short useful signal results for the measurement of the background absorption. This useful signal is very much influenced by the mains frequency and the amplitude of the mains voltage.
A very strong magnetic field is required for splitting the spectral lines by the Zeeman effect which ensures a clear separation of emission lines and absorption lines. To achieve this a strong exciting current has to be generated in the winding of the electromagnet. In the prior art atomic absorption spectrometers this current is generated from the mains voltage. The power requirement of the electromagnet which causes the Zeeman effect in the prior art atomic absorption spectrometers is quite high. This causes, among others, an undesired heating up.